Not that I do anything with flow dynamics...
I installed a superquiet bathroom exhaust fan recently. At first, I ignored directions and slapped it in with available ducting. (Manual? we don't need no stinking manual!) Huh, louder than the one it replaced! So I read the manual. For optimum performance, it needs 2 to 3' of straight ducting before turning to exit. OK, did that. SOB, it's quiet. I suppose it needs the straight to achieve laminar flow and possibly momentum.
OK, to reduce resistance to the intake you need to reduce surface variation. Micro pockets of vacuum and pressure causes areas of high velocity and low. Read friction. you want gradual change not sudden. HTHS.